Process for refining and deodorizing petroleum fractions



United States Patent corporation of Ohio No Drawing. Filed Feb. 17, 1961, Ser. No. 39,906 13 Claims. (Cl. 208-489) This invention comprises an improved process for the refining of mineral oils or petroleum fractions which contain a substantial quantity of mercaptans. More particularly, this invention is concerned with a process for refining and deodorizing sour petroleum fractions by treatment with an organic acid or acid anhydride in the presence of polyphosphoric acid.

Petroleum fractions, e.g., naphthas, kerosines, gasolines, fuel oil, lubricating oil, waxes, etc., as normally obtained from petroleum often have unsatisfactory odor characteristics resulting from the presence of malodorous mercaptans. The removal of these malodorous constituents has often proved difficult by original refining procedures. In the past, the removal of mercaptans has been accomplished to some extent by clay treating and by treatment with chemicals which form readily extractible derivatives. In some cases, the removal of mercaptans has been impractical and the sour petroleum fractions have been treated by a sweetening process in which the mercaptans are converted to odorless disulfides.

In the past, petroleum fractions have been treated with a variety of chemicals for producing odor-free products. Napthas have been treated with absorbents of various types and have been treated with various amines during distillation to prevent formation of malodorous constituents. Petroleum fractions have been subjected to solvent extraction with various acidic materials such as sulfur dioxide, phenol, and concentrated organic acids to extract color-forming and odor-forming constituents; see Spaght Patent 2,110,311. In Jezl Patent 2,927,077, a process is described in which a mineral oil fraction is treated with an organic acid or other acylating agent in the presence of an esterification catalyst to esterify color-forming bodies present in the oil.

It is therefore one object of this invention to provide a new and improved process for refining and deodorizing mercaptan-containing petroleum fractions by treatment with materials which convert mercaptans into odorless materials.

A feature of this invention is the provision of a process in which a sour petroleum fraction is treated with a lowmolecular-weight organic acid, acid anhydride, acid chloride, ester, or amide, together with a small amount of polyphosphoric acid, for a time in a range from about 30 minutes to 5 hours or more, which is sufficient to convert the mercaptans to odorless materials.

Other objects and features of this invention will become apparent from time to time throughout the specification and claims as hereinafter related.

In measuring the relative odor of petroleum products it has not been possible to develop a precise, quantitative measure of odor which is entirely independent of the individual who evaluates the odor. Nevertheless, there are certain procedures for rating odors which have been used in the petroleum industry. Odor evalution standards and methods have been proposed by a joint committee of the ASTM and TAPPI. Modification of this procedure has been used extensively in the evaluation of the odor of commercial petroleum products. In a typical petroleum company, an odor panel is selected consisting of several, e.g., to 20 or more, individuals who have been tested for their ability to discriminate between and match different odors. One test for selecof acid per mol of mercaptan in the fraction,

3,l20,48 6 Patented Feb. 4, 1964 tion of panel members involves series of chemical odors such as very dilute odors of acetic acid, phenol, toluene, and benzene. A second test involves a matching of a variety of different naphthas by odor from a single manufacturing source. A third test involves the matching of minteral spirits obtained from different manufacturers. By use of these screening tests it is possible to select a panel of 10 to 20 individuals who are especially discriminating in evaluating odors of petroleum products. In the rating of odors of petroleum fractions such as an odorless naphtha, a numerical rating scale has been established to describe odor quality.

Odor quality correctly matohin g a Numerical rating:

When evaluating the odor of petroleum naphthas the following procedure is used. The members of the odor panel are requested to avoid contact with contaminating odors, e.g., smoking, etc., for at least /2 hour prior to the test. The odor evaluation is carried out in an airconditioned room, at about E, which is as free as possible from extraneous odors. Each member of the test panel rates the odor of a product separately. A non-member of a panel conducts the test and is present to record any pertinent comments made regarding the odor. To eliminate bias, the product samples are coded, and the panel members are told the type of product being rated. To avoid odor fatigue, no more than three samples are rated at any one time. Any additional ratings are spaced by at least three hours. A total of seven panel members rate the product and the average of these opinions is reported as the odor rating.

In preparing the naphtha for odor evaluation, a 35-ml. representative portion is poured into a clean, odor-free, eight-ounce French square bottle. The bottle is sealed with a clean, odor-free screw-on cap. The same sample is used by all members of the panel. The type bottle used in the evaluation is the same as used in the screening tests for selection of the panel member. The panel member evaluates the odor of the naphtha by removing the cap from the bottle, placing his nose at the bottle mouth and snifling the odor. He checks the intensity of odor and for any foreign or undesireable odor that may be present and then numerically rates the odor using the above described scale. This method is called the wetodor of the naphtha.

In carrying out this invention, we have found that it is possible to convert sour naphthas and other petroleum fractions containing mercaptans to products having a very good or excellent odor rating. In accordance with our process, the mercaptan sulfur content and the odor of sour petroleum fractions can be drastically reduced by treating the fraction with an organic acid, acid anhydride, acid chloride, ester, or amide, in the presence of polyphosphoric acid at elevated temperatures. In our process, a sour petroleum fraction is mixed with an organic carboxylic acid or acid anhydride, in an amount of at least 2-5 mols together with about 2-5 mols of polyphosphoric acid per mol of mercaptan, and heated with agitation to a temperature of about l50400 F. for a period of 30 minutes to 5 hours or more, preferably 250350 F. for 2 to 4 hours. The length of time of reaction is inversely proportional to the reaction temperature so that the treatment may be terminated at relatively short periods of time at higher reaction temperatures.

In carrying out this treatment, the polyphosphoric acid used is a commercial product consisting of a liquid mixture of polymeric phosphoric acids having a P content in the range of about 72 to 90%, preferably about 82 to 84%. The carboxylic acid used in this treatment can be any stable, low-molecular-weight, organic (C -C monocarboxylic or (Cg-C12) dicarboxylic acid. These acids are preferably parafiinic acids, either branchedor straight-chain, although aromatic acids can be used. The acids can contain other substituents, or unsaturated bonds, as long as they are stable in the temperature range of about 150400 F. The acids used are preferably those containing up to about 12 carbon atoms per molecule and include propionic acid, butyric acid, hexanoic acid, decanoic acid, dodecanoic acid, benzoic acid, phthalic acid, succinic acid, sebacic acid, etc., and anhydrides thereof. In this process we can also use materials which yield acids upon reaction with impurities, such as water, in the hydrocarbon fraction, e.g., acyl amides, acyl chlorides, esters, etc.

After the reaction has gone to completion, the polyphosphoric acid is allowed to settle and is separated and recovered for re-use. Then the treated fraction is washed with water to remove unreacted acid. Preferably, the washed fraction is further neutralized, as with sodium bicarbonate, and the fraction is again washed with water. In some cases, an oil-insoluble thiolester separates from the fraction so that the treated material is not only improved in odor but the sulfur content is also reduced. This process is applicable to the treatment of any petroleum fractions, including sour naphthas, gasolines, kerosines, fuel oils, waxes, etc.

The following non-limiting examples are illustrative of the scope of this invention.

EXAMPLE I In one experiment, a crude petroleum distillate having a boiling range of 300330 F., a positive doctor test and a poor odor (No. 9) was treated in accordance with this invention. A ZOO-cc. portion of the distillate was mixed with 103.6 g. of polyphosphoric acid (82-84% P 0 and 5 cc. of propionic acid. The mixture was stirred and heated at about 300 F. for two hours. Thereafter, it was allowed to cool and the polyphosphoric acid was separated. The treated hydrocarbon phase was washed sequentially with Water, 5% sodium bicarbonate solution, and again with water. At this point, the doctor test showed that the product was sweet. The treated product was evaluated for odor by five associates, each of whom assigned to it an odor rating of 3.

EXAMPLE II In another experiment a 125-cc. portion of the raw distillate used in Example I was mixed with 25.1 g. of polyphosphoric acid and 2 cc. of propionic acid. The mixture was heated to 175 F. with stirring for two hours. Thereafter, the mixture was cooled and the hydrocarbon phase separated. The hydrocarbon phase was washed sequentially with water, sodium bicarbonate solution, and again with water. This product was found to have a very slightly positive doctor test and an odor rating of 5.

A series of additional experiments were carried out in which it was shown that reduction in ordor and in mercaptan content of a sour naphtha requires treatment With both an organic acid and polyphosphoric acid.

EXAMPLE III In one experiment, a 500-cc. flask, equipped with a stirrer and thermometer, was charged with 100 g. of sour distillate (odor No. 9), 2 g. succinic acid, and l g. p-toluene sulfonic acid. The mixture was heated to 300 F. for 4 hours. The hydrocarbon phase recovered from this treatment had a positive doctor test and no improvement in odor. This experiment shows that while treatment with an organic acid and an acylation catalyst may improve the color of the hydrocarbon fraction, it has no significant effect on odor.

EXAMPLE IV To 100 g. of sour distillate were added 25 g. of polyphosphoric acid. The mixture was stirred and heated to 300 F. for 2 hours. Afterwards, the reaction mixture was cooled, water-washed, and the product checked for odor improvement. The doctor test was positive. The odor of the product was rated at No. 10.

EXAMPLE V To 100 g. of sour distillate (odor No. 9) were added 25 g. of phosphorus pentoxide and 2 cc. of propionic acid. The mixture was stirred and heated to 300 F. for two hours. On heating, the phosphorus pentoxide formed a hard, almost crystalline material which clogged the stirrer somewhat. Afterwards, the product was cooled, waterwashed, and the hydrocarbon phase checked for odor improvement. The doctor test was positive and the odor of the product was rated at 7.

EXAMPLE VI In another experiment, the procedure of Example V was followed except that an equivalent amount of phosphoric acid was substituted for phosphorus pentoxide. In an evaluation of the treated product, it was found that the doctor test was positive and the product had an odor rating of 9.

In these experiments the odor evaluation was made by five of our associates. Each person rated the treated samples in the same order from good to poor odor. The treated samples each came from the same base stock and so different kinds or types of odor did not enter into the judgment, only odor intensity. This fact, together with the similar rating by each person, shows that there is a marked difference in odor intensity between the samples.

When our process is used in the treatment of other bydrocarbon fractions, it is possible to reduce both sulfur content and odor level by a substantial amount.

EXAMPLE VII When various petroleum fractions are treated following the procedure of Example I, a substantial odor improvement is obtained as indicated in Table I.

Table I Amount of Reagents (-g. portion) Organic Acid Tcmp., Time, Fraction Trcatcd 1 hr.

PPA, g. Organic Acid, g.

Gasoline propionic 10 3 300 3 succinic 25 3 350 2 phthalic" 25 3 275 5 butyric 15 2 350 2 succinic 15 5 300 3 phthalic l5 5 300 3 anhydridc. propionic 25 3 300 4 (1 25 3 350 3 Do 25 3 350 4 Lubricating Oil. 25 5 450 3 D0 25 5 400 4 Do 25 5 400 4 Stoddard Solvent propionic. 25 3 300 3 Do -do l5 3 350 3 Do phthalic 25 3 350 3 anhydridc. Do benzoic 20 3 300 3 In each case the treatment is effective to reduce the odor from an initial value of 9-10 to a value of 1-4.

While we have described our invention fully and completely with special emphasis upon several preferred embodiments, we Wish it to be understood that within the pe of the appended claims this invention may be practiced otherwise than as specifically described.

The embodiments of the invention in which an exclusive property or privilege is claimed are as follows.

We claim:

1. A method for refining and deodorizing a sour petroleum fraction containing a substantial quantity of mercaptans which comprises heating said fraction to a temperature of about 150-400 F. in admixture with polyphosphoric acid having a P content of about 82-84% and a compound selected from the group consisting of stable, loW-molecular-weight organic carboxylic acids, and their anhydrides, in an amount not less than about 2 mols of each acid per mol of mercapton, with agitation for a time not less than about /2 hour, sufiicient to convert said Inercaptans to odorless materials, separating the polyphosphoric acid from the treated petroleum fraction, and washing the treated fraction with water.

2. A process in accordance with claim 1 in which the organic acid is a monocarboxylic acid.

3. A process in accordance with claim 1 in which the organic acid is a dicarboxylic acid.

4. A process in accordance with claim 2 in which the organic acid is a C -C aliphatic acid.

5. A process in accordance with claim 2 in which the organic acid is a mononuclear aromatic acid.

6. A process in accordance with claim 3 in which the organic acid is a C C aliphatic acid.

7. A process in accordance with claim 1 in which the acid reactant is an acid anhydride.

8. A method of refining and deodorizing a sour petroleum fraction containing mercaptans which comprises heating said fraction to a temperature of about 250-350 F. in admixture with a lower alkanoic acid and polyphosphoric acid having a P 0 content of about 82-84%, in an amount of each acid not less than about 2 mols per mol of mercaptan, with agitation, for a period of about 2-4 hours sufficient to convert the mercaptans to odorless materials, separating the polyphosphoric acid, and Washin g the treated fraction with water.

9. A process in accordance with claim 8 in which the alkanoic acid is propionic acid.

10. A process in accordance with claim 8 in which the alkanoic acid is butyric acid.

11. A process in accordance with claim 8 in which the alkanoic acid is succinic acid.

12. A method of refining and deodorizing a sour petroleum fraction containing mercaptans which comprises heating said fraction to a temperature of about 250-350 F. in admixture with benzoic acid and polyphosphoric acid having a P 0 content of about 82-84%, in an amount of each acid not less than about 2 mols per mol of mercaptan, with agitation, for a period of about 2-4 hours sufficient to convert the mercaptans to odorless materials, separating the polyphosphoric acid, and washing the treated fraction with water.

13. A method of refining and deodorizing a sour petroleum fraction containing mercaptans which comprises heating said fraction to a temperature of about 250 -350 F. in admixture with phthalic acid and polyphosphoric acid having a P 0 content of about 82-84% in an amount of each acid not less than about 2 mols per mol of mercaptan, with agitation, for a period of about 2-4 hours sufiicient to convert the mercaptans to odorless materials, separating the polyphosphoric acid, and washing the treated fraction with water.

References Cited in the file of this patent UNITED STATES PATENTS 1,853,920 Morrell Apr. 12, 1932 2,027,648 Morrell Jan. 14, 1936 2,162,992 Ault et al. June 20, 1939 2,257,078 Soday Sept. 23, 1941 2,762,750 Slaughter et al Sept. 11, 1956 2,927,077 Jezl Mar. 1, 1960 OTHER REFERENCES Moeller: Inorganic Chemistry, John Wiley & Sons, Inc., New York (1952), pages 630-648. (Copy in Patent Ofiice Scientific Library.)

Remy: Treatise on Inorganic Chemistry, vol. I; Elsevier Publishing Company, New York (1956), pages 629-637. (Copy in Group 130.) 

1. A METHOD FOR REFINING AND DEODORIZING A SOUR PETROLEUM FRACTION CONTAINING A SUBSTANTIAL QUNATITY OF MERCAPTANS WHICH COMPRISES HEATING SAID FRACTION TO A TEMPERATURE OF ABOUT 150*-400*F. IN ADMIXTURE WITH POLYPHOSPHORIC ACID HAVING A P2O5 CONTENT OF ABOUT 82-84% AND A COMPOUND SELECTED FROM THE GROUP CONSISTING OF STABLE, LOW-MOLECULAR-WEIGHT ORGANIC CARBOXYLIC ACIDS, AND THEIR ANHYDRIDES, IN AN AMOUNT NOT LESS THAN ABOUT 2 MOLS OF EACH ACID PER MOL OF MERCAPTON, WITH AGITATION FOR A TIME NOT LESS THAN ABOUT 1/2 HOUR, SUFFICIENT TO CONVERT SAID MERCAPTANS TO ODORLESS MATERIALS, SEPARATING THE POLYPHOSPHORIC ACID FROM THE TREATED PETROLEUM FRACTION, AND WASHING THE TREATED FRACTION WITH WATER. 